There are at present two systems for electric guitars using guitar to synthesizer or guitar to MIDI controllers (MIDI meaning musical instrument digital interface). Both these systems have problems relating to playing technique. These problems are so serious that experienced electric and non-electric guitar players find them a major obstacle to overcome in order to get satisfactory playing results on either system alone. Such guitar players have to actually unlearn their normal guitar playing style and relearn a special playing technique for each system.
The first and oldest of these systems has six playing strings scanned or wired together at one end to form, in effect, one contact of a switch. Each fret, over which the strings pass, is divided into six segments which are electrically insulated and function as six switch contacts, one switch contact for each string. There are upto twenty-four such frets along the neck of the guitar providing one hundred and forty four string/fret intersections or switches. A set of two string/fret switches are closed when a selected string is pressed by a finger of the left hand of the guitar player between the respective segments of the selected adjacent frets. The selected fret nearer the bridge of the guitar determines the note being played. This first system has a number of problems.
Firstly, the segmented fret assemblies require six electrical wires for each fret. With twenty-four frets, a total of one hundred and forty-four wires are required for the neck wiring harness. This harness is difficult to manufacture; further, these wires and fret connections are virtually unrepairable once assembled inside the guitar neck. Thus, it is virtually impossible to replace a worn fret without replacing the whole wiring harness and all the frets.
Secondly, as these fret segments are simple logic switches, notes played on this system cannot be "bent" or drifted, a musical effect that electric guitar players consider to be essential. It is generally agreed that note bending is one of the most important characteristics that make the guitar unique and identifiable in popular music.
Thirdly, with the more basic versions of this system there is no possibility of other player expression such as use of the pick. As soon as a string touches a fret a note begins, ignoring completely whatever the guitar player's right hand may be doing. This also applies to right hand pick expression or "velocity" since all picking functions are totally ignored, this first system being unable to respond to use of the pick by the guitar player.
The second system has a magnetic pick-up head mounted near the bridge over which the six strings are tensioned and supported. This pick-up head feeds a pitch follower circuit of some sort, such as a pitch to voltage or pitch to MIDI arrangement. There are several main problems with this second system.
Firstly, it takes too long to determine the pitch of each note being played. The laws of physics dictate the maximum speed with which this can be done. A minimum of two valid samples, spaced apart in time of the lowest frequency component of each note has to be obtained in order to define a note. Even if all operation headroom time is removed, the act of pitch determination alone takes so long that almost all guitar players find it too slow.
Secondly, each note on each string has an entirely different harmonic structure. This harmonic structure also changes radically for any note as a function of how hard the note is picked, where on the string it is picked, what note was previously picked on the string, and what other notes are ringing on other strings. Further, the harmonic structure also changes radically for any note as a function of the time that note is held. In addition, the dominant frequency component of a guitar note is almost never the desired lowest frequency, but the second harmonic above it, i.e. the harmonic above the fundamental harmonic. This dominant component also changes as the note decays. This tends to make the pitch follower or pitch detection systems unstable and unreliable; they not infrequently find the wrong note, or jump to wrong notes as the actual notes decay. This necessitates very careful and deliberate playing technique to get even minimal results. This again means that the musician must unlearn his style and relearn a special cautious playing technique if he wishes to control a synthesizer via the guitar.
Thirdly, a great deal of circuitry such as tracking filters, automatic gain compensators, limiters, gain control stages and precision rectifiers are required for each string, making production of this circuitry expensive and physically too large to fit into the guitar body itself. Typically massive, and more unreliable, connection cables are required between the guitar controller itself and the rest of the system support circuitry.
Further, arbitrary decisions must be made using amplitude sensing in determining when a note is "on", and then "off". If the note on threshold is too high, some or even many notes are missed. On the other hand, if the "note on" threshold is too low, false notes and various noises appear as artifacts of normal playing. Since playing style may vary even during one song, and this threshold is set throughout the song, this presents a problem second only to pitch detection lag and errors.
Thus, both these current electric guitar systems have different problems that restrict the playing ability and performance of accomplished guitarists.